This invention relates to an on-demand four wheel drive system and, more particularly, to a rear axle viscous coupling differential assembly for such a system.
Part-time on-demand four wheel drive systems employing viscous clutch drive-line arrangements are known in the prior art. One such arrangement, found on the front-wheel drive VW Golf vehicle, is called a Synchro 4-wheel drive system. This system is disclosed on page 5 of the Sept. 15, 1985 issue of the publication Ward's Engine Update as using two separate viscous couplings. One viscous coupling is connected in the longitudinal propeller shaft for dividing the torque between the front and rear wheels if the front wheels are in a slip condition. A second viscous coupling is associated with a conventional bevel gear rear axle differential to provide limited slip between the vehicle rear wheels.